Coat a 1 1/2-quart souffl dish with cooking spray; sprinkle with 1/4 teaspoon sugar. Set aside.
Combine cocoa and hot water in a bowl. Stir well; set aside.
Melt margarine in a small, heavy saucepan over medium heat.
Add flour; cook 1 minute, stirring constantly with a whisk.
Add milk, 1/4 cup sugar, and salt; cook 3 minutes or until thick, stirring constantly.
Remove from heat.
Add cocoa mixture; stir well. Spoon into a large bowl; let cool slightly.
Beat egg whites (at room temperature) at high speed of a mixer until foamy.
Add 3 tablespoons sugar, 1 tablespoon at a time, beating until stiff peaks form. Gently fold 1 cup egg white mixture into cocoa mixture; gently fold in remaining egg white mixture. Spoon into prepared souffl dish.
Bake at 375 for 35 minutes or until puffy and set.
Remove from oven; serve warm, at room temperature, or chilled with Warm Turtle Sauce.